DEFORMATION MECHANISM AND STABILITY ANALYSIS OF A HIGH SLOPE AT PORTAL OF COMPRESSED TUNNELAT SHALLOW DEPTH

This paper examines a high slope at the portal of a compressed highway tunnel with shallow depth in south Anhui province. The construction design of zero excavation is proposed to maximally protect the geological environment and prevent the large-scale geological disasters. The necessary reinforcement measures are used by taking intco consideration of the site engineering geological conditions. The site engineering geological conditions are investigated systematically. Then the types and causes of rock mass structures and the combination between structural planes and slope surface are studied in detail so as to analyze the slope deformation mechanism. A geological model of this high slope is described with engineering geological profile. The detailed descriptions of the geological sketches are conducted. It is demonstrated that the slope deformation is always initiated by the non-uniform compression of the unconsolidated rock mass, leading to ladder sliding along the combination between structure planes with high dip angles and structure planes with low dip angles paralleling with slope. The ladder sliding makes greater stress to the structures and surrounding rocks of the tunnel. Failures can occur when the supplementary pressure exceeds their strengths, which will induce great geohazards. The result of FLAC3D numerical modeling indicates that the stress concentration distributes along the unconsolidated rock mass near the inside of this tunnel. The tensile stress zone can occur in the upper rock mass. Based on the analysis, before tunnel excavation, reinforcement measures should to be implemented to avoid stress concentrations on the tunnel structure and surrounding rocks.